Max Ground Pressure / Bearing Capacity

[drawyennik]

I'm jacking up a large electric mining shovel (1.5m lbs) and am wondering what a safe bearing capacity would be?

The pad is built out of 3-4" rock with a layer of compacted 3/4" crush on top.

 

[BigH]

How thick is your pad? What type of soil is underlying the pad?

 

[cvg]

what is the bearing area of the tracks / feet on the existing shovel? Back calculate the bearing pressure exerted by the tracks on the ground. Provide enough jacks and cribbing to maintain a bearing pressure equal or less than the pressure on the tracks.

 

[msquared48]

Those tracks are sitting on a concrete strip footing from what I see.

Look to the footing dimensions and reinforcing, if known, to get a bearing approximation, which may be lower for an isolated as opposed to strip condition.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[ishvaaag]

1.5 kgf/cm2 is safe in most not bad grounds. Your base seems not a bad ground, being crushed rock; maybe you can get 5 kgf/cm2 without problems.

However the coarse quality of the rock base may mean some tilt may happen. To forestall this I would try to (jack?) brace the machine against sidewise displacement.

 

[drawyennik]

Pad thickness
3-4" is 3 feet
3/4" is 1 foot

Under the pad is rock (see picture)

Yah i know the ground pressure exerted by the tracks (48.9 psi) but i dont want to have to put that much cribbing under my jacks b/c we need to be able to work in there.

In the first picture the shovel is on the pad (no concrete)

 

[SirAl]

At 0.9m of 75 to 100mm rock with 0.3m of 20mm crush topping; you should have 200kPa brg easy. The photos are a good attribute.

 

[oldestguy]

I'd do some trial and error jacking.

If, as you jack, you see displacement, just increase the bearing area and try again. Displacement of your granular mat is likely to be instantaneous or near that. I'd keep the mat as thin as possible, since you have rock below.

Then, once you find the situation does not move, at each support, you supplement it with say 50 percent added area support nearby each main support.

Consider what is safe when working under a car. You don't depend on any hydraulic other mechanical lift, but supplement with jack stands. Do the same here.